Advanced glycation end products as biomarkers for cardiovascular disease: browning clarifying atherogenesis

Methylglyoxal: A Key Factor for Diabetic Retinopathy and Its Effects on Retinal Damage

Background: Diabetic retinopathy is the most common retinal vascular disease, affecting the retina's blood vessels and causing chronic inflammation, oxidative stress, and, ultimately, vision loss. Diabetes-induced elevated glucose levels increase glycolysis, the main methylglyoxal (MGO) formation pathway. MGO is a highly reactive dicarbonyl and the most rapid glycation compound to form endogenous advanced glycation end products (AGEs). MGO can act both intra- and extracellularly by glycating molecules and activating the receptor for AGEs (RAGE) pathway. Conclusions: This review summarizes the sources of MGO formation and its actions on various cell pathways in retinal cells such as oxidative stress, glycation, autophagy, ER stress, and mitochondrial dysfunction. Finally, the detoxification of MGO by glyoxalases is discussed.

Cardiovascular risks and endothelial dysfunction in reproductive-age women with endometriosis

Endometriosis is a prevalent gynecological condition, affecting around 10% of reproductive-age women. Inflammatory processes associated with endometriosis may contribute to endothelial dysfunction. Increased skin accumulation of advanced glycation end-products (AGEs), reflecting arterial stiffness, potentially links endometriosis with elevated risk of cardiovascular events. We hypothesized that patients with endometriosis have impaired endothelial function as well as increased arterial stiffness and AGE skin accumulation, compared to healthy controls. We compared endothelial function, arterial stiffness, and levels of AGEs in patients suffering from endometriosis and in healthy controls. The study included 45 women aged 20 to 40: 21 patients with endometriosis and 24 healthy controls, matched in terms of age, BMI, and blood pressure values. Endo-PAT 2000 device was used for non-invasive assessment of (i) endothelial function, expressed as Reactive Hyperemia Index (RHI), and (ii) arterial stiffness, expressed as Augmentation Index (AI) and Augmentation Index at 75 heart beats/min (AI@75). Endothelial dysfunction was defined as an RHI value ≤ 1.67. AGE Reader device was used for non-invasive evaluation of skin AGE level accumulation. Patients with endometriosis had lower mean RHI values (1.69 ± 0.54 vs. 2.02 ± 0.48, p = 0.037) and a higher prevalence of endothelial dysfunction, (52.4% vs. 20.8%, p = 0.027) compared to healthy controls. Skin AGE level was higher in patients with endometriosis, compared to controls (2.00 ± 0.57 vs. 1.70 ± 0.24, p = 0.013). There were no significant differences in AI and AI@75 between the two groups. Patients with endometriosis have impaired endothelial function and higher AGE skin accumulation, which are well-established preclinical manifestations of increased cardiovascular risk. There is a great need for comprehensive cardiovascular risk assessments in women with endometriosis to prevent the development of potential atherosclerotic-based complications.

Mediterranean Diet Adherence, Physical Activity, and Advanced Glycation End Products in Complex PTSD: A Comprehensive Examination of Lifestyle and Cardiovascular Risk in War Veterans

As accumulated evidence suggests that individuals with post-traumatic stress disorder (PTSD) encounter earlier and more frequent occurrences of cardiovascular diseases, the aim of this study was to ascertain the differences in lifestyle and cardiovascular risk between PTSD and complex PTSD patients. We enrolled 137 male war veterans with PTSD (89 had complex PTSD). The diagnosis was established based on 11th revision of International Classification of Diseases (ICD-11), and cardiovascular risk was estimated by the measurement of advanced glycation end products. Adherence to Mediterranean diet (MD) was lower in the complex PTSD group (2.2% vs. 12.5%, p = 0.015). Accordingly, patients with complex PTSD had lower healthy lifestyle scores in comparison to PTSD counterparts (50.6 ± 9.7 vs. 59.6 ± 10.1, p < 0.001), and a positive association was noted between MD adherence and a healthy lifestyle (r = 0.183, p = 0.022). On the other hand, differences were not noted in terms of physical activity (p = 0.424), fat % (p = 0.571) or cardiovascular risk (p = 0.573). Although complex PTSD patients exhibit worse adherence to MD and lower healthy lifestyle scores, these differences do not seem to impact physical activity, body composition, or estimated cardiovascular risk. More research is needed to clarify if this lack of association accurately reflects the state of the PTSD population or results from insufficient statistical power.

Trapping Methylglyoxal by Taxifolin and Its Metabolites in Mice

Trapping of methylglyoxal (MGO), an important precursor of advanced glycation end products (AGEs), is considered an effective therapy for alleviating AGE-induced chronic metabolic diseases. In this paper, taxifolin (Tax) was first found to effectively trap MGO by forming mono- and di-MGO adducts under in vitro conditions. In addition, the mechanism of trapping MGO by Tax was also studied in vivo. Tax was demonstrated to efficiently trap endogenous MGO via formation of mono-MGO adducts in urine and fecal samples of C57BL/6J mice after oral administration of Tax and MGO. Mono-MGO adducts of Tax metabolites, including methylated Tax, aromadendrin, quercetin, and isorhamnetin, were identified in C57BL/6J mice urine and fecal samples by ultra-high-performance liquid chromatography coupled to quadrupole time-of-flight tandem mass spectrometry (UHPLC-QTOF-MS/MS). One mono-MGO-Tax was purified from the in vitro reaction mixture, and its structure was elucidated as 6-MGO-Tax based on the analysis of UHPLC-QTOF-MS/MS and detailed nuclear magnetic resonance (NMR) data. Quantification studies demonstrated that Tax and its metabolites trapped MGO in a dose-dependent manner in C57BL/6J mice urine and fecal samples. Furthermore, we also detected mono-MGO adducts of Tax and methylated Tax in urine and fecal samples of diabetic db/db mice after oral administration of Tax. Taken together, our results demonstrated that dietary Tax has the potential to detoxify MGO and treat AGE-associated chronic diseases.

AGEs-Induced and Endoplasmic Reticulum Stress/Inflammation-Mediated Regulation of GLUT4 Expression and Atherogenesis in Diabetes Mellitus

In recent decades, complex and exquisite pathways involved in the endoplasmic reticulum (ER) and inflammatory stress responses have been demonstrated to participate in the development and progression of numerous diseases, among them diabetes mellitus (DM). In those pathways, several players participate in both, reflecting a complicated interplay between ER and inflammatory stress. In DM, ER and inflammatory stress are involved in both the pathogenesis of the loss of glycemic control and the development of degenerative complications. Furthermore, hyperglycemia increases the generation of advanced glycation end products (AGEs), which in turn refeed ER and inflammatory stress, contributing to worsening glycemic homeostasis and to accelerating the development of DM complications. In this review, we present the current knowledge regarding AGEs-induced and ER/inflammation-mediated regulation of the expression of GLUT4 (solute carrier family 2, facilitated glucose transporter member 4), as a marker of glycemic homeostasis and of cardiovascular disease (CVD) development/progression, as a leading cause of morbidity and mortality in DM.

Urolithin A alleviates advanced glycation end-product formation by altering protein structures, trapping methylglyoxal and forming complexes

Urolithin A (UroA) is a first-in-class natural compound derived from the gut microbiota-derived metabolites of ellagitannins. This research for the first time evaluates the mechanisms of UroA inhibiting advanced glycation end-product (AGE) formation by fluorescence spectroscopy, molecular docking, liquid chromatography (LC) and LC-Oribitrap tandem mass spectrometry. The results indicated that UroA exhibited a good suppression effect on the formation of AGEs in human serum albumin (HSA)-fructose and HSA-methylglyoxal (MGO) systems. Further mechanism analysis revealed that UroA alleviated AGE formation by changing the conformational structure of HSA, trapping reactive MGO to form mono-MGO-UroA complexes, promoting the exposure of chromophores to a more hydrophobic micro-environment, and forming stable UroA-HSA complexes. UroA bound with HSA in an equimolar manner, the binding was an exothermic spontaneous process, subdomain IIIA was the preferred binding pocket, and hydrogen bonding, hydrophobic interactions and van der Waals forces were the major interaction forces. The number of glycation sites detected in glycated HSA was reduced by 1 and 2, respectively, when 181.82 and 363.64 μM UroA was added. These could provide an insight into the mechanism of UroA inhibiting HSA glycation, and highlight its value as a promising glycation inhibitor in the prevention of diabetic complications.

Methods to assess advanced glycation end-products

PURPOSE OF REVIEW

Advanced glycation end-products (AGEs) resulting from protein glycoxidation constitute biomarkers of interest in different pathological situations. Several methods for quantifying AGEs in biological fluids or tissues have been developed without any real consensus on a gold standard method. The aim of this review is to provide an overview of recent publications in the field helping to decide if these markers could find their place as diagnostic tools in clinical practice.

RECENT FINDINGS

This update shows that new AGEs are regularly discovered and new analytical methods (especially mass spectrometry-based methods) regularly described. Skin autofluorescence measurement is increasingly performed due to the practicability of the dedicated devices, in spite of its questionable specificity. In biological fluids, carboxymethyllysine remains the most frequently measured AGE. However, to date, it is still difficult to compare results obtained from different studies because measured AGEs and modes of expression are different and because no method standardization has been initiated.

SUMMARY

Despite their potential interest as biomarkers and the availability of unfortunately non-standardized assay methods, AGEs remain confined to clinical research studies without really being used in daily clinical practice. These challenges must be addressed in order to allow their implementation.